Polyquinoxalines and method of preparation

ABSTRACT

Linear polyquinoxalines are produced by the reaction of an aromatic quinoxaline having two furan endcaps or substituents with an aromatic olefinic end-capped monomer. These linear polymers have an alicyclic endooxy linkage repeated throughout the polymer backbone chain where the furan end-cap combines with the olefin end-cap by Diels-Alder reaction. The linear polymer is converted to a higher performance polymer by heating in a range of 200* to 400*C whereupon the endooxy linkage is aromatized in situ. The polyquinoxalines so prepared are suitable for use in severe environments at temperatures up to 350*C.

United States Patent Jones Sept. 16, 1975 [54] POLYQUINOXALINES AND METHOD OF 3,661,850 5/ 1972 Stille 260/50 PREPARATION 3,746,687 7/1973 Duffy et .al 260/50 Inventor: Robert J. Jones, Hermosa Beach,

Calif.

Assignee: TRW lnc., Redondo Beach, Calif.

Filed: Oct. 31, 1973 Appl. No.: 411,513

US. Cl... 260/47 UA; 117/124 E; 117/161 UN; 161/203; 161/247; 260/30.2; 260/30.8 DS; 260/32.6 N; 260/33.4 P; 260/33.6 UA;

Int. Cl. C08f 5/04 Field of Search 260/47 UA, 49, 63 N, 79

References Cited UNITED STATES PATENTS 2/1972 Augl 260/50 4/1972 Aug] et al. 260/50 Primary ExaminerLester L. Lee Attorney, Agent, or FirmDaniel T. Anderson; Alan D. Akers; Willie Krawitz [5 7] ABSTRACT polymer is converted to a higher performance polymer by heating in a range of 200 to 400C whereupon the endooxy linkage is aromatized in situ. The polyquinoxalines so prepared are suitable for use in severe environments at temperatures up to 350C.

2 Claims, No Drawings POLYQUINOXALINES AND METHOD OF PREPARATION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 45 USC. 2457).

BACKGROUND OF THE INVENTION Polyquinoxalines have been prepared by heating slowing a tetraminc and a bisglyoxal in an inert atmosphere at about 250C. The resulting polymer produced by this method is more insoluble than'polyquinoxalines produced using other methods; 7

When a solvent medium is employed, equimolar' amounts of bisglyoxal and a tetramine are reacted at elevated temperatures under an inert atmosphere, and 20 the polymer precipitates from solution.

Generally, polyquinoxalines have been synthesized from bisglyoxals which had either a hydrogen or a phenylene radical end-cap. Polyquinoxalines which had the hydrogen radical end-cap on the bisglyoxal generally exhibited less thermal stability but better adhesive properties than polyquinoxalines having the phenylene end-cap ,on the bisglyoxal.

Polymer solubility at high linear molecular weights presented another problem for the prior art polyquinoxalines. This is particularly true for the polymer solubility of the polyquinoxalines. However, by proper selection'of monomers having flexible connecting groups between the aromatic units, solubility of polyquirioxalines below about 400C is improved over polyquinoxalines synthesized from monomers having a greater proportion of aromatic uni-ts.

SUMMARY OF THE INVENTION High performance polyquinoxalines are produced by the in situ aromatization of polyquinoxalines, which have an alicyclic endooxy linkage in the polymer chain. The linear polymer-is produced by the reaction of an aromatic difui'an end-capped monomer with an aro-' matic monomer terminated in diolefin. For example, reaction" of 2;3-di-a-furylquinoxalines with 1,3 dimaleimidobenzene may beillustrated as follows:

l i .c U a;

The intermediate linear polymer containing the endooxy bridge provides a structure having a relatively low melting point which permits easier processability prior to final cure by in situ aromatization. Upon subse-' quent fabrication, the polymer is heated to aromatize the endooxy bridge as follows:

-Co'ntinued The polyquinoxalines described herein offer an economic advantage over prior quinoxaline resins because of the simplicityof the Diels-Alder synthesis of relatively low cost ingredients. In addition, water, a nontoxic byproduct, is evolved in the aromatization DESCRIPTION OF THE PREFERRED. EMBODIMENTS Polyquinoxalines having outstanding performance characteristics are produced by the polymerization of an aromatic difuran end-capped monomer and an aromatic diolefin end-capped monomer. The reaction between the end-caps produces an alicyclic endooxy linkage in the polymer chain which gives good solubility and fabrication characteristics to the intermediate polymer. Upon fabrication to the final product, heat is applied which results in the in situ aromatizatioh of the alicyclic endooxy linkages and the accompanying loss of water. The resulting aromatized polymer has improved performance characteristics manifested by reduced solubility, improved chemical and thermal stability, and improved physical strength.

The polymerization process is initiated by mixing cquimolar amounts of an aromatic quinoxaline monomer having two furan end-caps with an aromatic monomer having two olefin end-caps. The olefin and the furan end-cap groups react at temperatures from 25 to 300C to produce a polyquinoxaline having recurring alicyclic endooxy linkages according to the following reaction:

where R is anaromatic quinoxaline radical selected from the following:

l N/ C\ J N\C/ H @K 1 ICH 1 w J H K w 6 C 0ntinued N FI t I and N N H I N H? x C'H where X is O, S-, CO-, SO CH-;. viscosity andmass'of the reactants will effect the poly- -C H C;,H merization time, alsosThe insitu aromatization is normally effected in a temperature range of between 200 and 400C. The aromatization reaction involves the g 3 same mechanism regardless of the constituents between the alicyclic endooxy linkages, and therefore, 2 the time and temperature relationships required remain substantially constant. However, where high molecular weight reactants as contrasted to low molecular weight and reactants are used, significantly different times and where E is a furan radical; E can be either a vinyl radical or a maleimido radical; R is a difunctional aromatic radical which may be selected from the following:

temperatures of reaction may be expected.

Although it is not critical, solvents may be used to reduce the viscosity of the reactants and facilitate mixing and fabrication. Generally, common solvents can be used, e.g., cresol, dimethylformamide, xylene, pyridine,

0 dimethylsulfoxide or N-methyl-Z-pyrrolidirie.

eeeooo o where E E is either and n is an integer between 4 and 200. After fabrication of the polymer to the final product configuration, the polymer is subjected to a thermal cure cycle which aromatizes the alicyclic endooxy linakge, according to the following reaction:

where E E R, R, and n have been defined previously, and E is The initial Diels-Alder polymerization reaction may be effected at or near room temperature. However, the preferred temperature range is where the reaction is between 100 to 300C. In other instance. the polymerization reaction will be completed within 24 to 96 hours. It should be understood that parameters such as .monomers which are not commercially available,

methods for synthesis of these compounds are well known and may be obtained from any standard treatise disclosing organic synthesis, e.g., Organic Synthesis, Vols. 1 through V, published by J. Wiley and Sons, New York City, N.Y.

The invention will be more clearly understood by referring to the following examples. These examples illustrate specific embodiments and should not be construed as limiting the invention.

EXAMPLE I Polymerization of 2,3-di-a:-furylquinoxaline and 1,3-dimaleimidobenzene A mixture of 2.098 g (0.008 mole) of 2,3-di-ozfurylquinoxaline and 2.146 g (0.008 mole) of 1,3- dimaleimidobenzene was heated at 232C (450F) for 4 hours under a pressure of 200 psig. The resulting polymer was a consolidated plug indicating melt polymerization had occurred. The polymer sample was then postcured employing a cycle consisting of 4hour linear heat-up from 204 to 3l5C followed by isothermal heating at 315C for 4 hours. The sample obtained from this experimentation was found to be stable to over 350C by thermogravimetric analysis.

EXAMPLE ll Polymerization of 2,3-di-a-furylquinoxaline and Bis(4-maleimidophenyl) methane A mixture of 2.098 g (0.008 mole) of 2,3-di-afurylquinoxaline and 2.86 g (0.008 mole) of bis(4- maleimidophenyl) methane was treated in the same fashion as described in Example I. The sample was stable to 325C by thermogravimetric analysis.

. EXAMPLE lll Polymerization of 2,3-di-a-furylquinoxaline and Bis(-4-maleimidophenyl) oxide A mixture of 2.098 g (0.008 mole) of 2,3-di-afurylquinoxaline and 2.883 g (0.008 mole) of bis(4- lected from the group consisting of maleirnidophenyl) oxide was processed as in Example I to give a solid polymer sample which was found to be stable to 335C by thermogravimetric analysis.

I claim: 1. A method for making polyquinoxaline polymers comprising:

A. reacting at temperatures ranging from to 300C, equimolar amount of (i) a difuran endcapped monomer having the formula C R l R C where v...,R' is a monofunctional radical selected from the group consisting of hydrogen and furan; when R is a furan radical, R is selected from the group consisting of when R is a hydrogen radical, R is selected from the group consisting of and where E is an olefinic radical selected from the group consisting of and whereby a linear polyquinoxaline is formed having alicyclic endooxy linkages in the linear chain; and

B. heating the polyquinoxaline in a temperature range of between 200 to 400C to convert the alicyclic endooxy linkages to aromatic linkages by in situ aromatization.

2. A polyquinoxaline consisting essentially of the structure:

where R is a difunctional aromatic quinoxaline radical selected from the group consisting of A W W i) H I 9 Y CN jjif c H DQ, H c nxc w N N H Cl N N H) C w N N H c c N N i c c and where X is selected from the group consisting of O., S, -CO-- the group consisting of and E is selected from the group consisting of 65 m C C I lll ld and and h is an integer from 4 to 200. 

1. A METHOD FOR MAKING POLYQUINOXALINE POLYMERS COMPRISING: A. REACTING AT TEMPERATURES RANGING FROM 25* TO 300*C, EQUIMOLAR AMOUNT OF (I) A DIFURAN END-CAPPED MONOMER HAVING THE FORMULA
 2. A POLYQUINOXALINE CONSISTING ESSENTIALLY OF THE STRUCTURE: -(E)-(R)-(E)-(R''))N WHERE R IS A DIFUNCTIONAL AROMATIC QUINOXALINE RADICAL SELECTED FROM THE GROUP CONSISTING OF 